Download Instructional Manual - FSU High Energy Physics

Instruction Manual
for
Franck-Hertz Apparatus
Model P67103
Pacific Science Supplies, Inc
1-800-530-1500
3. Specifications
Instruction Manual
for
Franck-Hertz Apparatus
1.
Voltage supplied to Franck- Hertz tube.
UG1K
1.3  5V
UG2A (rejecting voltage)
1.3  15V
UG2K point- measure observe
0  100V
Sawtooth wave on oscilloscope
0  50V
UH (filament voltage)
AC: 3V,3.5V, 4V, 4.5V,
5V, 5.5V, 6.3V.
2.
Parameter about sawtooth wave.
Scanning Voltage
0  50V
Scanning Frequency
115 ± 20Hz
Voltage amplitude of scanning output
 1V
3.
Low-current Measuring range
Model P67103
1. Applications
The Franck-Hertz Apparatus (Model P67103) is designed for college students
to demonstrate the existence of quantized states. The experiment can be
performed in less time because the use of argon tube eliminates the heating of a
tube. The data can be recorded manually, or directed to an oscilloscope or
computer for display.
2. Identification
The controls on the panel of the device are shown in Fig.1.
4
3
9
5
4.
6
10
5.
16
10-9  10-6 A(4 steps)
Observable numbers of spectrum amplitude
Point – measuring
5
Observe on universal oscilloscope
2
Operating condition
Ambient temperature
Relative humidity
Operating power
Preheating time
Continuous operating time
Rated input power
Dimensions
-10  40C
85%(40C)
AC 220V ± 22V, 50Hz
5 min
8 hours
15W
1 X b X hmm: 400 X 230 X 130
15
4.Working Principle
1
2
11
7
12
14
The Franck-Hertz tube in this instrument is a tetrode filled with argon.
Figure 2 describes the symbols of every electrode and relations between voltages.
8
13
Fig.1
1
Milliameter
4
Scan Control
7
Voltage Range Selector
10 0-100V Adjustment
13 Y-output Terminal
16 Observation Window
2
5
8
11
14
Voltmeter
Filament Voltage Selector
1.3 –5V Adjustment
Power Indicator
Ground
3
6
9
12
15
Manual/Auto Switch
Current Multiple Selector
1.3–15V Adjustment
Power Switch
X-output Terminal
Fig.2
A voltage of about 1.5V is added between the first grid (G1) and the cathode
(K) to dismiss the effect of space charge on cathode scattering electrons.
When the filament is heated, the electrons transmitted by the cathode oxide
are accelerated in the electric field between the second grid (G2) and the cathode,
obtaining more and more energy. But at the beginning, because of the low
voltage between the second grid and cathode, the electron energy is low. Thus
the energy exchanged is little even if the electrons collide with the atom. So the
plate current IA formed by electrons penetrating the second grid will increase
with the increase of UG2K. (segment OA in Figure 3)
5. Operations
1.
2.
3.
4.
5.
Switch on the power. The indicator will flash.
Turn the “Manual-Auto” switch to “Manual”, rotate the Scan knob counterclockwise to end, turn “Filament Voltage Selector” to 3.5V, “Current
Multiple” selector to 10-7.
Turn “Voltage Stepper” to 1.3  5V, and rotate 1.3  5V adjust knob until
the voltmeter reads 1.5V to set UG1K 1.5V.
Turn “Voltage Stepper” to 1.3  5V, and rotate 1.3  5V adjust knob until
the voltmeter reads 7.5V to set UG2A 7.5V (rejecting voltage).
Turn “Voltage Stepper” to 0  100V, and rotate 0  100V adjust knob until
the voltmeter reads 0V to set UG2k 7.5V(accelerating voltage).
When you have finished step 2 ~ 5, with UH=3.5V (Filament voltage), UG1K
= 1.5V (the voltage between the first grid and kathode), UG2A =7.5V( The
voltage between the second grid and anode) you are ready to do the
experiment These are suggested voltages for the experiment. You can do the
experiment by parameters marked on the argon tube either.
Fig. 3
When UG2K reaches the first excitation potential of the argon atom,
electrons collide with argon atoms near the second grid (it is a non-elastic
collision), and transfer total energy obtained in the accelerating field to argon
atoms, exciting them from ground state to the first excitation state. But electrons
themselves, transferring all energy to argon atoms, can’t overcome the reverse
field. They are drawn back to the second grid even if some of them penetrated
the second grid. So the plate current IA decreased obviously. Then, with the
increase of UG2K, the electron energy increased too. There will be enough energy
left after the collision with argon atom. Thus they can overcome the reverse field
and reach plate A. And at this time current IA begins to increase again, until UG2K
is 2 times the voltage of argon atom’s first excitation potential, when electrons
between G2 and K lost energy again because the second non-elastic collision
causes the second decrease of acceleration voltage UG2K
Let UG2K be the horizontal ordinate and IA the vertical axis. We can plot the
spectrum amplitude curve. The voltage difference between two consecutive
valley point (or peak point) is the first excitation potential of argon atom. This
experiment illustrates the fact that the slow electrons in Franck-Hertz tube collide
with argon atoms, excite the atoms from low level to high level. By measuring
the argon’s first excitation potential (13.1V, which is constant) We can verify
that the energy absorbed and transmitted is discrete, not continuous.
6.
7.
8.
Turn off the power, move the top cover of the instrument, place the FranckHertz tube in lamp socket, replace the top cover and turn on the power The
indicator will flash. Preheat 3 minutes, before the experiment.
Rotate “ 0  100V” adjust knob, and at mean time observe the variation of
rheometer and voltmeter’s readings. With the increase of UG2K (accelerating
voltage), the rheometer’s reading appears peak and valley periodically.
Record the corresponding voltage and current. Let the output current be the
vertical ordinate, and UG2K the horizontal ordinate. Plot the spectrum
amplitude curve.
Turn “Manual-Auto” switch to “Auto”, and connect the instrument’s Y,
ground, X socket to Y, ground, X of a student oscilloscope. Put the scanning
range switch of oscilloscope to “external X”. Switch on the power of
oscilloscope, adjust the Y and X shift to make the scan baseline on the
bottom of screen, aand adjust X Gain” to make scan baseline 10 grids.
Rotate the scanning knob of this instrument, and observe the waveform on
the oscilloscope’s screen. Adjust the “Y gain” and “X gain” of the
oscilloscope’s attenuation to make the waveform clear and Y amplitude
moderate. Rotate scanning potentiometer clockwise to end, set the
maximum scan voltage to 50V, measure the horizontal distance of two
consecutive crest ( count the grids). Multiply the distance by 5V/grid, to
obtain the value of argon atom’s first excitation potential.
6. Caution
1.
2.
3.
During the experiment, pay attention to the output current indicator when the
voltage is over 60V. If the rheometer’s reading increases suddenly, decrease
the voltage at once to avoid the damage to the tube.
If you want to change the value of UG1K, UG2A and UH during the experiment,
rotate the “0 ~ 100V” adjust knob counter-clockwise to end, before making
the changes.
The filament voltage of this instrument is 3V, 3.5V, 4V, 4.5V, 5V, 5.5V,
6.3V. You can do the experiment with these filament voltages. If skewness
occurred on the top of waveform (that means the anode output current is too
strong and causes the amplifier to distort), the filament voltage should be
decreased.
7. Packing List
1.
2.
3.
4.
5.
Franck-Hertz Apparatus
Argon Tube
Connect wires of power
Connect wires of host machine and oscilloscope
Operating instruction manual
1 each
1 each
1 each
1each
1 each